Evolution in the design of "clean rooms" has resulted in the general use of modular filter units that can be incorporated into customized or standard plenum structures. The general function of this assembly is to subject all the air coming into a room to the action of high-efficiency filters to remove all airborne particles in excess of a specified size. A completely site-constructed plenum, where parts are all cut from stock and processed at the point of installation, is always expensive, as the use of special machinery and cutting fixtures common in factory operations is not practical. This situation has resulted in the development of larger and larger fully prefabricated filtration modules including the plenum and its structure that supports the filter units. There comes a limit to this line of development, however, and this is due to the problems and cost involved in shipping large units from the factory to the point of installation, and then securing them in place. Widths have a practical maximum of eight feet, due to highway restrictions. Handling a structure this wide, three or four feet high, possibly over twenty feet long and weighing several tons, can easily dissipate the efficiency resulting from factory construction.
It is now clear that this process of design evolution must take a new turn. Other industries, faced with this same problem, have tended to shift over to prefabricated components readily assembled on site without extensive machining or processing. This results in handling components of more reasonable size, and vastly increasing the load density on trucks by removing the need to transport large volumes of the empty space within the modules. The present invention is directed at the formation of a structure capable of this type of construction at a high order of efficiency, while still complying with strict clean air requirements that forbid leakage around the filter units. These modules must be able to accommodate suspension from various ceiling structures, and have a wide range of design flexibility with regard to providing units of different sizes from essentially the same components.